A soy sauce is one of Japanese traditional condiments, which is obtained through heat denaturation of either soybeans alone or a combination of soybeans and grains such as cereals, moisture adjustment, inoculation and culturing of a koji mold therein to make a soy sauce koji, addition (mixing) of an aqueous common salt solution thereto to make a soy sauce moromi, fermentation and maturation, press-filtration to make a clear liquid, and pasteurisation (sterilzation under heating). In the present invention, a soy sauce obtained in such a manner refers to “brewed soy sauce”.
Brewed soy sauce requires a long period of time for the process of fermentation and maturation of 3 to 10 months. During this period, unique color, taste, and flavor are provided due to the action of various enzymes and microorganisms in a soy sauce koji and a soy sauce moromi. In particular, the flavor is known to consist of 300 types or more of components, which are complexly combined with each other to give off a unique savor of soy sauce. A compound known as one of these flavor components, namely 4-hydroxy-2(or 5)ethyl-5(or 2)methyl-3(2H)-furanone (hereunder, referred to as HEMF) is a representative characteristic soy sauce smell contained in brewed soy sauce. A higher content of this component is likely to provide a favorable soy sauce.
Therefore, various methods for increasing HEMF have been so far examined and developed (refer to Patent documents 1 to 3).
However, in recent years, consumer needs have been diversified, and demands for soy sauce having a reduced soy sauce smell have been increasing. To comply with such needs, various methods for reducing the soy sauce smell are examined and developed (refer to Patent documents 4 to 6), which however involve problems in that the manipulation is cumbersome and that the cost is incremented for industrial practice. Moreover, another method is also known in which HEMF serving as a high boiling component of soy sauce is efficiently removed by decompression, absorption, or the like. However, this method involves problems in that HEMF can not be solely and selectively removed, and as a result, the soy sauce quality is notably deteriorated, and that the cost is incremented.
Incidentally, since HEMF is generated and accumulated by soy sauce yeast fermentation, an effective means for avoiding the generation and accumulation of HEMF in a soy sauce moromi is to suppress the growth of the soy sauce yeast. As an extreme example thereof, a technique is also proposed in which a soy sauce moromi is digested at a high temperature for a short time to suppress the yeast fermentation so as to obtain a soy sauce-like seasoning liquid (Non-patent document 1).
However, such types of moromi prepared by the suppression of yeast fermentation and soy sauce yeast non-fermented moromi obtained by the short time and high temperature digestion have drawbacks such as strong smells of raw materials and smells of warmed brew, inferior masking abilities, defective alcohol contents due to almost nonperformance of alcohol generation and accumulation, problematic fungal resistance, and lower utility values as condiments.
Moreover, juice of a soy sauce moromi obtained by the suppression or nonperformance of yeast fermentation is difficult to expect to have a yeast-derived delicate taste, and provides a monotonous savor lacking in feeling of maturity.
Therefore, it is considered that the accomplishment in the suppression of HEMF generation and accumulation without suppressing yeast fermentation would enable to provide a superiorly versatile soy sauce having a matured umami taste of soy sauce remaining as it is, a yeast-derived delicate taste, unnoticeable smells of raw materials, and a solely reduced soy sauce smell.
Incidentally, in the production of a brewed soy sauce, various flavor components contributing to the rich flavor of soy sauce are mainly generated and accumulated by soy sauce yeast, and are also referred to as “brewed flavor”. In particular, alcohol-based flavor components such as methionol are highly correlated to the yeast fermentation, and are known to have effects of reducing smells of raw materials such as steam-boiled soybeans and roasted and milled wheat and smells of soy sauce koji, and effects of eliminating (masking) unpleasant smells of various ingredients and seasoning materials, when used as a condiment (Non-patent document 2).
For such reasons, it is considered to greatly contribute to the soy sauce brewing industry if remarkable amounts of brewed flavors such as methionol can be generated and accumulated by soy sauce yeast fermentation, and if, conversely, HEMF serving as a “characteristic flavor” of a brewed soy sauce can be suppressed as much as possible.
However, generally, the contents of methionol and HEMF are linked with each other in a brewed soy sauce. A soy sauce having less HEMF has less methionol, while a soy sauce having a plenty of methionol has a plenty of HEMF. This means that HEMF and methionol are both derived from the fermentation of soy sauce yeast, and it is difficult to reduce HEMF alone while maintaining methionol in the production of a soy sauce with a conventional process for producing a brewed soy sauce.
In a process for producing a brewed soy sauce, a soy sauce moromi subjected to an appropriate yeast fermentation contains about 20 to 150 ppm of HEMF and concurrently contains about 1.0 to 3.0 ppm of methionol per 1.0% (W/V) of total nitrogen (Non-patent document 3).
However, such a brewed soy sauce has a strong soy sauce smell, which is not suitable for the application to processed foods that are desired to have neither soy sauce-like nor soy sauce-derived flavor.
In this way, with a conventional process for producing a brewed soy sauce, it has been considered to be absolutely impossible and has never been carried out to produce a soy sauce having reduced HEMF while maintaining methionol.
Meanwhile, as a soy sauce having no HEMF, an amino acid soy sauce obtained through degradation of defatted soybeans with hydrochloric acid, neutralization with alkali, and subsequent press-filtration is known. However, this soy sauce has a peculiar amino acid smell in accordance with the degradation with hydrochloric acid, and does not contain HEMF nor methionol due to the nonperformance of yeast fermentation. Accordingly, such an amino acid soy sauce has a common purpose with the present invention in the point of not having HEMF, however it is different from the soy sauce of the present invention in the point of not having methionol. Thus, these two types of sauces are clearly distinguished.    Patent document 1: JP Patent Publication (Kokai) No. 3-183490 A (1991)    Patent document 2: JP Patent Publication (Kokai) No. 5-176781 A (1993)    Patent document 3: JP Patent Publication (Kokai) No. 6-277083 A (1994)    Patent document 4: JP Patent Publication (Kokai) No. 5-115261 A (1993)    Patent document 5: JP Patent Publication (Kokai) No. 9-271351 A (1997)    Patent document 6: JP Patent Publication (Kokai) No. 2004-141014    Non-patent document 1: Soy sauce library First series, written by Ichiro NAGASE, issued on Jun. 1, 1967, p. 29    Non-patent document 2: Numazu Industrial Research Institute of Shizuoka Prefecture Report No. 8, November, 2000, “Development of novel seasoning using microorganisms”    Non-patent document 3: “Science and technology of soy sauce, Enlarged edition”, written and edited by Shinrokuro TOCHIKURA, enlarged on Mar. 31, 1994, p. 285